1. Field of the Invention
This invention relates generally to a pattern preliminary processing system used mainly for recognition of patterns such as a printed character and a hand-written character, and more particularly relates to pattern preliminary processing system in which a signal representative of an arbitrary pattern is tri-valued and the resulting tri-valued signal is converted into a bi-valued signal with reference to one- or two-dimensional information peripheral thereto.
2. Description of the Prior Art
The optical character reader for recognizing printed characters and hand-written characters generally comprises a pre-processing unit for bi-valuing pattern signals picked up by such a pattern input device as the pick-up tube or flying spot scanner and thinning and normalizing the resulting bi-valued pattern, and a recognizing unit for extracting features from the normalized bi-valued pattern and for comparing the features thereof with those of a standard pattern thereby to recognize an unknown input pattern by detection of an agreement therebetween.
In the conventional preliminary processing system, it is common practice to obtain a bi-valued pattern from a pattern signal derived from an image pick-up device by dividing the pattern signal at a predetermined threshold level into a character part above the threshold represented by "1" and a background part under the threshold represented by "0". In the case where the original paper carries a stain or smear or the characters are partially broken, however, the stained or smeared portion may present itself as 1 and the broken portion as 0 erroneously, with the result the bi-valued pattern may be broken or distorted or noise is generated which is liable to be confused with part of the character, thus making it impossible to produce a bi-valued pattern high in quality.
Further, in the event that the shade of a character is different at different parts thereof, a bi-valued pattern associated therewith has portions different in thickness. Also, if one portion of the background is different in brightness from the other portion, it may be difficult to accomplish a bi-valuing process by limiting the characters to 1 and the background to 0.